TL16C550D_09 Datasheet, PDF (39/54 Pages) Texas Instruments – ASYNCHRONOUS COMMUNICATIONS ELEMENT WITH AUTOFLOW CONTROL

TL16C550D, TL16C550DI
www.ti.com .................................................................................................................................................. SLLS597E – APRIL 2004 – REVISED DECEMBER 2008
• Bit 7: This bit is the complement of the data carrier detect (DCD) input. When the ACE is in the diagnostic test
mode (LOOP [MCR4] = 1), this bit is equal to the MCR bit 3 (OUT2).
Programmable Baud Generator
The ACE contains a programmable baud generator that takes a clock input in the range between dc and 16 MHz
and divides it by a divisor in the range between 1 and (2¹⁶ – 1). The output frequency of the baud generator is
sixteen times (16×) the baud rate. The formula for the divisor is:
divisor = XIN frequency input ÷ (desired baud rate × 16)
Two 8-bit registers, called divisor latches, store the divisor in a 16-bit binary format. These divisor latches must
be loaded during initialization of the ACE in order to ensure desired operation of the baud generator. When either
of the divisor latches is loaded, a 16-bit baud counter is also loaded to prevent long counts on initial load.
Table 9 and Table 10 illustrate the use of the baud generator with crystal frequencies of 1.8432 MHz and 3.072
MHz respectively. For baud rates of 38.4 kbits/s and below, the error obtained is small. The accuracy of the
selected baud rate is dependent on the selected crystal frequency (see Figure 27 for examples of typical clock
circuits).
Table 9. Baud Rates Using a 1.8432-MHz Crystal
DESIRED
BAUD RATE
50
75
110
134.5
150
300
600
1200
1800
2000
2400
3600
4800
7200
9600
19200
38400
56000
DIVISOR USED
TO GENERATE
16× CLOCK
PERCENT ERROR
DIFFERENCE BETWEEN
DESIRED AND ACTUAL
2304
1536
1047
0.026
857
0.058
768
384
192
96
64
58
0.69
48
32
24
16
12
6
3
2
2.86
Table 10. Baud Rates Using a 3.072-MHz Crystal
DESIRED
BAUD RATE
50
75
110
134.5
150
300
600
1200
DIVISOR USED
TO GENERATE
16× CLOCK
PERCENT ERROR
DIFFERENCE BETWEEN
DESIRED AND ACTUAL
3840
2560
1745
0.026
1428
0.034
1280
640
320
160
Copyright © 2004–2008, Texas Instruments Incorporated
Submit Documentation Feedback
39
Product Folder Link(s): TL16C550D TL16C550DI